For example, Patent Literature 1 listed below discloses a conventional technique of producing a partially-reduced iron by packing carbon composite pellets on a moving grate and thermally reducing the pellets, the carbon composite pellets not being coated with a carbon material for combustion.
However, the technique described in Patent Literature 1 has the following problems and a partially-reduced iron with a high degree of reduction cannot be obtained.
(1) After being dried, the carbon composite pellets are ignited with a gas torch and air is made to flow therethrough to combust and heat the carbon composite pellets. Accordingly, a portion of a packed bed of the carbon composite pellets on a side into which air flows keeps on combusting and reduction dose not proceed in this portion. Moreover, even if the reduction proceeds, the carbon composite pellets are reoxidized by air and thus the degree of reduction does not improve at all. Moreover, since a high temperature state is maintained, a molten slag is excessively generated and an operation may thereby become difficult in some cases.
(2) The pellets having moved out of a carbonization area is heated by a high-temperature inert gas whose oxygen concentration is equal to 5% or less and metallization proceeds by using a remaining portion of the carbonaceous material. However, the amount of remaining carbon is small and the degree of metallization is low. Moreover, until a lower portion of the packed bed reaches a high temperature, an upper portion of the packed bed is exposed to oxidant gases such as carbon dioxide and water vapor generated from the high-temperature carbonaceous material, causing reoxidation of the upper portion to proceed.
(3) A high-temperature gas in a metallization area where a large amount of heat is required is produced by combusting part of a flammable volatile component in the coal which is generated in the carbonization area and CO gas which is generated by the reduction reaction. However, since the amount of flammable components is small with respect to the amount of the entire exhaust gas, a supplementary fuel is additionally required.
In view of the problems above, for example, Patent Literatures 2 and 3 each disclose a conventional technique of producing partially-reduced iron in which pellets formed by mixing and pelletizing a reduction carbon material, a fine iron ore, and a slag-forming flux are added with a carbon material for combustion by coating the pellets with the carbon material for combustion, the carbon material for combustion is ignited, and then the pellets are subject to sintering with air being suctioned downward.